The development of molecular diagnostics has revolutionized care in most medical disciplines except infectious disease, where they have failed to play a widespread, transforming role. The reliance on slow culture methods is particularly frustrating in the current crisis of antibiotic resistance as the development of molecular tools to rapidly diagnose the inciting pathogen and its drug resistance profile would transform the management of bacterial, fungal, viral, and parasitic infections, guiding rapid, informed drug treatment in an effort to decrease mortality, control health care costs, and improve public health control of escalating resistance among pathogens. In U.S. hospitals alone, 1.7 million people acquire nosocomial bacterial infection and 99,000 die every year, with 70% of these infections due to bacteria resistant to at least one drug at estimated annual cost of $45 billion (Klevens et al., 2002. Public Health Rep. 2007; 122(2):160-6; Klevens et al., Clin Infect Dis. 2008; 47(7):927-30; Scott, “The Direct Medical Costs of Healthcare-Associated Infection in U.S. Hospitals and the Benefits of Prevention.” In: Division of Healthcare Quality Promotion NCfP, Detection and Control of Infectious Diseases, editor. Atlanta: CDC, 2009). However, the problem is not limited to the U.S. and microbial resistance now impacts the majority of common bacterial infections globally. Global spread of methicillin-resistant S. aureus (MRSA), multi-drug resistant tuberculosis (MDR-TB), and increasingly drug resistant Gram-negative organisms prompted the formulation of an action plan focusing on surveillance, prevention and control, research and product development (US action plan to combat antimicrobial resistance. Infect Control Hosp Epidemiol. 2001; 22(3):183-4). However, minimal progress has been made on any of these fronts.
Prompt administration of the appropriate antibiotic has repeatedly been shown to minimize mortality in patients with severe bacterial infections, whether within the hospital setting with nosocomial pathogens such as E. faecium, S. aureus, K. pneumoniae, A. baumanii, P. aeruginosa, and Enterobacter species, or in resource-poor settings with pathogens such as tuberculosis (TB) (Harbarth et al., Am J Med. 2003; 115(7):529-35; Harries et al., Lancet. 2001; 357(9267):1519-23; Lawn et al., Int J Tuberc Lung Dis. 1997; 1(5):485-6). However, because current diagnostic methods involving culture and sub-culture of organisms can take several days or more to correctly identify both the organism and its drug susceptibility pattern, physicians have resorted to increasing use of empiric broad-spectrum antibiotics, adding to the selective pressure for resistance and increasing the associated health-care costs. A point of care diagnostic to rapidly (e.g., less than 1 hour) detect pathogens and their resistance profiles is urgently needed and could dramatically change the practice of medicine. Some effort into designing DNA- or PCR-based tests has resulted in tools that are able to identify pathogens rapidly with low detection limits. However, global use of these tools is currently limited due to cost and demand for laboratory infrastructure and to the inherent insensitivity of PCR-based methods in the setting of crude samples that are not easily amenable to the required enzymology. Molecular approaches to determining drug resistance have been even more limited, available for some organisms (e.g., MRSA, TB) in very limited ways, based on defining the genotype of the infecting bacteria relative to known resistance conferring mutations. This method however, requires fairly comprehensive identification of all resistance conferring single nucleotide polymorphisms (SNPs) for the test to have high sensitivity (Carroll et al., Mol Diagn Ther. 2008; 12(1):15-24).
One key limitation to broad adoption of molecular diagnostic tests in clinical infectious disease is the inhibitory effects of bodily fluids such as blood upon many of the reactions required for molecular detection. Isolating or enriching pathogens away from host cells would greatly numerous downstream detection and characterization assays, such as nucleic acid hybridization or amplification tests that could be used to determine the identity or antibiotic susceptibility of the pathogen.